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Your keto numbers
Every calculator that hands you 5% of your calories as carbs is running the sum backwards. Ketosis answers to absolute grams, so a 5% rule gives a 240 lb man twice the carbohydrate of a 130 lb woman and calls them both keto. Here you set the gram ceiling and everything else is built around it.
Week one drains your glycogen, and glycogen leaves with about three times its weight in water. We put a number on that parcel, subtract it, and plot both lines so you can see what actually came off you. This is the reason keto looks like a miracle on day five and a failure on day twelve.
Keto's blind spot. The moderate-protein convention rests on a gluconeogenesis worry the evidence does not support, and the bill is paid in lean tissue. Your starting number scales with lean mass and climbs as you get leaner. Drag it down to the classic range if you want, and the page tells you what it costs.
Fat gets whatever calories are left once carbs and protein are paid for, which makes it a ceiling rather than a quota to chase. Nobody needs to drink butter to reach a percentage. Move either slider and watch fat absorb the difference in real time.
Keto flu is sodium and potassium walking out the door, not detox. You get milligram targets for sodium, potassium and magnesium on your results page, plus the blood pressure caveat, instead of a vague nudge to drink more water on day four when it is already too late.
No email gate, no $37 custom keto plan on the next screen, no exogenous ketone affiliate links. It runs entirely in your browser and nothing you type ever leaves your device.
Age, height, weight and how much you move. Pounds and feet by default, kilograms and centimeters if you prefer, and we show the conversion under each field either way so you never have to go look it up.
Six descriptions per sex, or hand us a DEXA figure or three tape measurements if you have them. Most people have never had a scan, and a description you can recognize in the mirror beats a formula that cannot tell muscle from fat. This sets your lean mass, and lean mass sets your protein.
From a thirty percent cut to a ten percent gain. It names what each setting means as you move it, and it refuses to hand you a deficit your fat stores cannot actually fund, however hard you drag.
Two more sliders live on your results: net carbs in grams, and protein scaled to your lean mass. Fat absorbs the difference and the pie redraws as you drag. Underneath, what the scale will do week by week, when ketosis shows up, and how much salt it takes to get there without a headache.
You want a number to eat to, and you would rather not meet the keto flu the hard way. Start at 20 g, read the electrolyte table before day two, and expect the scale to lie to you for a couple of weeks.
It did not stop. The water left, and what you are watching now is the real rate, which was always the real rate. The chart draws exactly this shape, which is usually enough to stop somebody quitting a thing that is working.
Fair worry, and mostly a protein problem rather than a carbohydrate one. Push the protein slider into the sports nutrition range and watch what happens to the lean tissue line in the projection.
Your glycogen refilled while you were off, so the week one drop happens all over again, and it is water all over again. Knowing that in advance stops you drawing the wrong conclusion in either direction.
Read the medication note at the bottom of your results before you change anything. SGLT2 inhibitors plus very low carbohydrate has caused ketoacidosis at normal blood sugar, and insulin doses usually need cutting within days. That is a conversation with your doctor, not with a web page.
Run the numbers before you clear out the pantry. Seeing 160 g of fat and 20 g of carbs written down tells you fairly quickly whether this is a way you would want to eat for six months.
Four numbers, and the sequence is the part almost every keto calculator gets wrong.
A ketogenic diet has exactly one defining feature: you eat little enough carbohydrate that your liver starts turning fatty acids into ketone bodies in quantity. Everything else is downstream of that. So the calculation opens with calories, fixes carbohydrate as a hard gram ceiling, sets protein from your lean mass, and hands fat whatever is left in the budget.
Read that back and notice what never happened. At no point did anyone decide the diet should be 75% fat. That number is a result, and it slides around depending on your size, your goal and how deep a deficit you are running. A calculator that opens by declaring 75/20/5 and works backward into grams produces carbohydrate targets that scale with bodyweight, which is incoherent: ketosis responds to the grams you eat, not to the share of your plate they happen to occupy.
Where the percentage approach breaks. Apply a 5% carb rule to two real people. A 130 lb woman eating 1,500 calories gets 19 g of carbs and lands in ketosis comfortably. A 240 lb man eating 3,000 gets 38 g and may well not, especially if he is sedentary. Same rule, opposite outcomes, and neither of them was ever asked what they were aiming for.
Below roughly 50 g a day, and dependably below 20 g, your liver runs short of glucose to hand out and starts producing ketone bodies instead. Blood beta-hydroxybutyrate crossing 0.5 mmol/L is the accepted definition of nutritional ketosis, and most people get there on day two to four. This is the only number in your whole plan that behaves like a real threshold. Miss it and you are on a low-carb diet, which is a perfectly respectable diet, but it is not the one you came here for.
Keto inherited a moderate-protein rule on the grounds that surplus amino acids get converted into glucose and knock you out of ketosis. The mechanism exists; the direction of causation does not. Gluconeogenesis is demand-driven, meaning your liver produces the glucose your body requests rather than manufacturing extra because supply turned up. What is real is the arithmetic. Carbs are capped and calories are fixed, so every gram of protein you add is a gram of fat you have to take away. Protein and fat are fighting over one budget, and this calculator shows you the moment that fight gets tight rather than quietly resolving it against your muscle.
Fat fills the gap, which makes it a ceiling with a floor underneath rather than a target to hit. Eating fat is not what puts you in ketosis; not eating carbohydrate is. Come in a little under on a day you were not especially hungry and you have simply run a slightly larger deficit, which is not a problem when the goal is losing fat. This is precisely where the butter-in-your-coffee era went wrong: people treated a remainder as a quota and bolted several hundred uncounted calories a day onto a diet they were trying to lose weight on.
Net carbs are the carbohydrate your body can actually put to use. On a US label that is a subtraction, and it is the one piece of keto label advice that is genuinely straightforward.
| Line on the panel | What it contains | What you do |
|---|---|---|
| Total Carbohydrate | Everything: starch, sugars, fiber and sugar alcohols, calculated by difference | Start here |
| Dietary Fiber | Largely unmetabolized, and already counted inside the line above | Subtract all of it |
| Sugar Alcohols | Also inside the total. Erythritol behaves like fiber, maltitol behaves like sugar | Subtract erythritol, count maltitol |
One caveat that matters more than it used to, now that half a pantry is imported. The subtraction is a US convention, not a universal one. Labels in the UK, the EU and Australia declare available carbohydrate only, with fiber listed separately beneath as a sub-line and already excluded from the headline number. Subtract fiber from one of those and you are removing something that was never in there, which costs you a slice of your daily allowance every single day. The tell is placement: if fiber is indented under the carb line as part of it, subtract. If it reads as a separate declaration, the work is already done for you.
Fiber itself is worth defending. It is the first casualty of a low carb ceiling, and at 20 g of net carbs you will not come close to the usual adult recommendation from food alone. Non-starchy vegetables, avocado, chia and flax buy you the most fiber per gram of net carb, which is the exchange rate that actually matters here.
If you are eating in a deficit, your split will probably land somewhere between 60 and 68% fat rather than the textbook 75%. Nothing has gone wrong. The textbook number describes somebody eating at maintenance, where every calorie they burn arrived on a plate.
In a deficit, part of your fuel is coming off your own body, and body fat is pure fat. Somebody eating 1,800 calories at 62% fat while running a 600 calorie deficit is actually burning 2,400 calories of fuel, of which 1,716 are fat. That is 71%. Their metabolism has no way of knowing which of it arrived by fork. This calculator reports both figures, because the dietary one is what you shop and cook to, and the effective one is what your liver is responding to.
Your muscles and liver hold carbohydrate as glycogen, and glycogen is stored wet: roughly three grams of water for every gram of glycogen. Stop eating carbohydrate and that entire parcel is released over about a week. For most adults it is 4 to 8 lb, and for a large muscular person it can be more.
This produces the most predictable emotional arc in dieting. Week one is spectacular. Week two looks like a stall. Neither reading is correct. The rate you see from week three onward is the real one, and it was the real one the whole time. It also means the weight walks straight back on the first time you eat a proper plate of pasta, which is not a relapse. It is a tank refilling.
The comparison nobody selling keto wants to run. When trials match calories and protein, ketogenic diets do not produce more fat loss than anything else. What keto genuinely has is appetite control: most people eat less on it without consciously trying, and a deficit you can hold beats a theoretically superior one you abandon. That is a real advantage worth having. It is just not a metabolic one, and anybody telling you carbohydrate itself made you fat is selling something.
Headache, fatigue, cramps, fog and a short fuse, typically days two through seven. It is not your body detoxing from sugar. When insulin falls, your kidneys stop retaining sodium and start excreting it, and potassium follows it out the door. The symptoms are the symptoms of mild dehydration and low sodium, because that is what they are.
The clinical groups with the most published ketogenic practice put the targets at 3,000 to 5,000 mg of sodium a day, which is roughly 1.5 to 2.5 teaspoons of table salt, alongside 3,000 to 4,700 mg of potassium and 300 to 500 mg of magnesium. Those numbers sit well above general population advice, on purpose, because the general population is not running on low insulin. Salt your food properly, drink a cup of broth on the afternoon of day two, and most of week one simply does not happen to you.
One exception to take seriously: if you have high blood pressure, heart failure or kidney disease, do not adopt a 5,000 mg sodium target from a website. Ask your doctor what your number should be, because for you this is not a harmless adjustment.
There is no reviewer byline on this page. Inventing a doctor to put a headshot beside would be worth less than showing the working, so here is every equation the calculator uses and where it came from.
| Step | What we use | Source |
|---|---|---|
| Resting metabolic rate | Mifflin-St Jeor by default; Katch-McArdle when you supply a measured body fat percentage and your BMI is 30 or below | Mifflin et al. 1990; Katch-McArdle / revised Cunningham 1991 |
| Maintenance calories | Resting rate multiplied by a five-step activity factor, 1.2 to 1.9 | Conventional activity multipliers. Broad steps, not measurements |
| Body fat from tape | US Navy circumference method, imperial regressions, every input converted to inches first | Hodgdon and Beckett 1984. Accurate to about 3 to 4 percentage points |
| Body fat without tape | Deurenberg BMI equation. Cannot separate muscle from fat, so it over-reads on lifters | Deurenberg, Weststrate and Seidell 1991 |
| Protein, sports nutrition setting | 2.3 to 3.1 g per kg of lean mass in a deficit, about 1.0 to 1.4 g per pound, rising as body fat falls | Helms et al. 2014, adopted verbatim by the ISSN protein position stand. The curve between those two bounds is our interpolation, not a published formula. |
| Protein, classic keto setting | 1.2 to 1.7 g per kg of lean mass, about 0.55 to 0.77 g per pound, scaled by activity | Conventional ketogenic practice. Offered because people on therapeutic protocols want it, not because we think it is the better default |
| Deficit ceiling | About 48.5 kcal per kg of fat mass per day, roughly 22 per pound, capped again at 1,000 kcal | Derived from Alpert's fat mobilization work, corrected for the unit error that circulates widely. Alpert's figure is per pound, not per kilogram |
| Calorie floor | The greater of 1,200 (women) / 1,500 (men) and 30 kcal per kg of lean mass, about 14 per pound | 2013 AHA/ACC/TOS prescription range, and the RED-S energy availability threshold. The second is the better grounded of the two |
| Glycogen water | 13 g of glycogen per kg of lean mass, about 5.9 g per pound, roughly 60% of it lost, each gram carrying 3 g of water | Olsson and Saltin 1970 for the water ratio. Shown as a range, because the ratio is contested and newer work argues it is lower. |
| Energy density | 7,700 kcal per kg of adipose tissue, which is about 3,500 per pound; 4/4/9 kcal per gram for carbohydrate, protein and fat | Standard constants. The 3,500 figure is a population average, not your personal exchange rate |
| Ketosis threshold | Blood beta-hydroxybutyrate at or above 0.5 mmol/L, with 0.5 to 3.0 covering nutritional ketosis | Standard clinical definition, consistent across the ketogenic literature |